The present invention is directed to integrated circuits. More particularly, the invention provides a method and device for an integrated circuit for a microphone interface. Merely by way of example, the invention has been applied to interface circuit for an electret microphone. But it would be recognized that the invention has a much broader range of applicability. For example, the invention can be applied to interface circuits to other kinds of microphones or interface circuits to other signal sources.
Voice and audio band applications often use a microphone to pick up the voice or audio energy from the environment and translate it into a voltage or current. Microphones are used in many applications such as telephones, tape recorders, hearing aids, multimedia productions, computers for recording voice, voice control interface for computers, VoIP, and other computer applications. A popular choice for the microphone is the ‘electret condenser’ type microphone. This microphone typically requires a DC bias to operate. An example is shown in FIG. 1, which is a schematic diagram of a conventional CODEC microphone interface circuit. As shown, electret microphone 102 often requires many off-chip components to interface with a CODEC integrated circuit 150. For example, microphone 102 is biased with resistors 112 and 114, and a capacitor 122 for a DC bias with noise and power supply filter. A gain stage is often used to interface with the CODEC chip 150. In FIG. 1, the gain stage includes discreet components such as capacitors 142, 144, 146, and 148, and resistors 132, 134, 136, and 138. Even though conventional interface circuit techniques have been in wide use, they suffer from many limitations, as discussed in more details below.
Therefore, an improved technique for microphone interface circuit is desired.